1. Field of the Invention
The present invention generally relates to a wireless communication apparatus and a wireless communication method. More particularly, the present invention relates to a wireless communication apparatus and a wireless communication method in which multipath interference is relieved.
2. Description of the Related Art
FIG. 1 shows an configuration example of a mobile communication system. The mobile communication system includes mobile stations 22 and a base station 23 which are placed in each area. In addition, there is an obstacle 24 which reflects radio wave of mobile wireless communication.
In this configuration, when the base station 23 radiates a radio wave to the mobile station 22, the radio wave is reflected by the obstacle 24 so that the direct wave 25 and the reflected wave 26 arrive at the mobile station 22 via a plurality of paths. This is called multipath.
In the mobile station 22, when the direct wave 25 and the reflected wave 26 arrive at the antenna, they interfere with each other. As a result, when the direct wave 25 and the reflected wave 26 have opposite phases, signals are attenuated significantly. When the direct wave 25 and the reflected wave 26 are in phase, signals are amplified.
The level of received wave in the mobile station varies significantly according to the position of the mobile station due to the interference caused by the multipath. It is known that the interference occurs by wavelength of the wave.
Conventionally, in order to decrease degradation of signal transmission quality due to attenuation caused by interference and to keep good receiving state, a space diversity system is adopted in which a plurality of antennas which are placed different positions and/or which have different directions are provided for receiving signals.
In addition, for example, when communication which uses spreading codes is performed and when the phases of the direct wave and the reflected wave are not completely opposite so that they are not completely canceled, a RAKE receive system is adopted in which a plurality of receive circuits are provided such that the phases of the direct wave and the reflected wave are adjusted when they are received.
Describing the RAKE receive more precisely, the multipath direct wave 25 and the reflected wave 26 shown in FIG. 1 are received in different time positions with respect to the time base shown as the direct wave 27 and the reflected wave 28 in FIG. 2. Thus, by adding delays to the direct wave 27 and the reflected wave 28 properly and synthesizing them, it becomes possible that a plurality of multipaths can be synthesized and received.
However, according to the above-mentioned system, since a plurality of antennas are necessary, there is a problem in that the size of the mobile station becomes large.
In addition, in the RAKE receive system, there is a problem in that it is difficult to prevent interference between the direct wave and the reflected wave caused in the antennas, and, interference between received codes at the time of demodulation.